Gluten biopolymers

ABSTRACT

This invention consists of a modified gluten biopolymer for use in industrial applications, such as composites and foams. In the present work, the fracture toughness of the gluten polymer was improved with the addition of a thiol-containing modifying agent. This work also resulted in the development of a gluten biopolymer-modified fiber bundle, demonstrating the potential to process fully biodegradable composite materials. Qualitative analysis suggests that a reasonably strong interface between the natural fibers and biopolymer matrix can form spontaneously under the proper conditions. Therefore this invention relates to a modified gluten biopolymer for use in industrial applications, such as composites, stabilized foams and molded articles of manufactures. The present invention relates to a new gluten based biopolymer with modified properties, such as an increase in impact strength, and prepared by using thiol-containing molecules. The multifunctional activity of the polythiol-containing molecules generates the potential for the development of a new material base for commodity plastics. The invention furthermore relates to a new composite material comprising gluten-coated fiber, its use and the method for preparing the composite material.

FIELD OF THE INVENTION

The present invention relates to a new gluten based biopolymer withmodified properties, like an increased impact strength, and prepared byusing polythiol-containing molecules. This invention also relates to amodified gluten biopolymer for use in industrial applications, such ascomposites, stabilized foams and molded articles of manufactures and tothe process for preparing the new gluten based biopolymer. The inventionfurthermore relates to a new composite material comprising gluten-coatedfiber, its use and the process for preparing the composite material.

BACKGROUND OF THE INVENTION

Current polymer production often involves the use of toxic solvents,which place workers at risk, damages the environment, and places a largeregulatory burden on government and companies alike. Water-based orsolid powder-based production of biopolymers and composites couldprovide enormous reductions in the toxic solvent load on workers and thesurrounding environment. This increased (environmental) awareness hasgiven the materials community impetus to develop cost-effectivebiomaterials with adequate mechanical properties. While research inrecent years has led to an improved understanding of the properties ofnatural fibers, the problem of identifying a cost-effective biopolymermatrix material or composite material with suitable properties remainsunresolved.

Plant proteins, such as for example wheat proteins, are interestingrenewable raw materials and already a wide variety of biopolymers basedon plant proteins has been used and investigated, alone or in mixtures,in order to obtain for example edible films and coatings. The plantproteins investigated include soy proteins, corn zein, wheat proteins,cotton seed proteins and pea proteins and can be considered asheteropolymers.

Wheat gluten is a mixture of monomeric proteins (gliadins) and“polymerized” proteins (glutenins) linked through intermoleculardisulfide bridges. The gluten proteins are largely implicated in theviscoelastic character of gluten and gluten proteins are responsible forgiving wheat flour dough its strength and visco-elastic properties.Wheat gluten can easily be isolated by removing starch and watersolubles by gently working a dough under a small stream of water. Afterwashing, a rubbery ball is left, which is called gluten. Next to thisprocess which is called “dough or Martin process” other isolationmethods exist like the “batter process”. Commercially available glutencontain approximately 75% protein, 10% carbohydrate, <10% moisture, 5%lipids and <1% minerals, but these amounts are variable. The glutenproteins are furthermore very rich in glutamine and proline.

There is already much literature on the use of gluten, also inindustrial applications. For example wheat gluten films have beenstudied in significant detail (Gennadios, A., and Weller, C. L., FoodTechnol. 1990, 44, 63-69; Gontard, N., et al., J. Food Sci. 1992, 57,190-195; Herald, T. J., et al., J. Food Sci. 1995, 60, 1147-1150; Roy,S. et al., J. Food Sci. 1999, 64, 57-60; Larré, C., et al., J. Agric.Food Chem. 2000, 48, 5444-5449). Many attempts have been made to convertwheat gluten or corn zein into a usable biodegradable polymer (Guilbert,S. et al., Food Add. Contam. 1997, 14, 741; Pommet, M. et al., Polymer2003, 44, 115; Redl, A. et al., Rheol. Acta 1999, 38, 311; Pouplin, M.et al., Agric. Food Chem. 1999, 47(2), 538-543; di Giola, L. et al.,Agric. Food Chem. 1999, 47, 1254). Films have been cast from glutenprotein dispersions in water under different pH conditions or inethanol. It was demonstrated that plasticizing agents could be used toimprove film flexibility and decrease brittleness (Ali, Y et al. Ind.Crops Prod. 1997, 6, 177-184). Indeed, researchers have observed thatthe preparation of wheat gluten films necessitates the use of aplasticizer. In the absence of a plasticizer, gluten films are brittleand difficult to handle. A number of plasticizers have been explored inthe past, including amines (diethanolamine and triethanolamine) andpolyhydroxy compounds (anhydrous glycerol, polyethyleneglycols, andpolypropyleneglycols). Typical concentrations range from 10 g to 60g/100 g of dry matter (Gennadios, A. and Weller, C. L., Food Technol.1990, 44, 63-69; Roy, S. et al., J. Food Sci. 1999, 64, 57-60). Fromthree known plasticizers (water, glycerol and sorbitol), water was foundto be the most effective plasticizer (Pouplin, M., et al., J. Agric.Food Chem. 1999, 47, 538). The action of a plasticizer is generally tointerpose itself between the polymer chains and alter the force holdingthe chains together. Polymer plasticization enables thus to reduce theshaping temperature of the thermoplastic process and to impart adequateflexibility to the material. However, it can also greatly influence thefunctional properties of the material (Pommet, M. et al., Polymer 2003,44, 115). In a more recent study, Pommet et al. explored the use offatty acids as a plasticizing agent for gluten (Pommet, M., Redl, A.,Morel, M. H., Guilbert, S., Polymer 2003, 44, 115). Theirthermo-mechanical data revealed a “compatibility limit” between thelipid and gluten, beyond which phase separation was observed.

The prior art describes methods for fractionating gluten into gliadinand glutenin (Midwest Grain U.S. Pat. No. 5,610,277) and attempts toform solid, non-edible biodegradable, grain-protein based articles(Midwest Grain U.S. Pat. No. 5,665,152), where the processes appliedalways involves cleaving of the disulfide linkages in the protein usingat least 0.01 by weigth of a reducing agent, selected from sodiumsulfite, sodium bisulfite, sodium metabisulfite or ascorbic acid andrespectively furthermore selected from alkali metal and ammoniumsulfites, nitrites, mercaptoethanol, cysteine, cysteamine and mixturesthereof. The formulation of U.S. Pat. No. 5,610,277 also includes fromabout 20-85% by weigth of grain protein, from about 5-75% by weigthstarch, up to about 14% by weigth water and from about 10-40% by weightof a plasticizer, such as glycerol. In the U.S. patent, also the mixingwith fibers is described. While some aspects of the work by MidwestGrain appear similar to our work, there are however several distinctdifferences. That is, the additive we propose in first instance not onlyreduces a number of the disulfide linkages in the protein, but they alsohave the potential to be covalently incorporated in the protein polymernetwork and crosslinking the proteins, thereby modifying the polymernetwork and as a consequence modifying the material properties.

It can be argued that the formation of covalent bonds is a necessaryfirst step in the development of a stable biopolymer system. Most of thestudies presented thus far have relied on plasticizers that, at best,form only hydrogen bonds with the gluten protein chains (see referencesabove). The use of chemical crosslinkers to modify the properties ofprotein-based materials have been reported as well, but to inducecrosslinking with the protein structure required either the use of acatalyst (Ghorpade, V. M. et al., Trans ASAE 1995, 38, 1805; Larré, C.,Agric. Food. Chem. 2000, 48, 5444) or an aggressive radiation treatment(Brault. D., Agric. Food. Chem. 1997, 45, 2964).

Thus, much research has already been undertaken in order to obtain agluten or zein based usable biodegradable polymer. However, all of theseapproaches encounter problems and a usable biodegradable polymer has notbeen described yet. For example, previously reported experiments,designed to improve the impact strength of the gluten material requirethe addition of at least 10-20% (w/w) of some plasticizer, such asglycerol or triethanolamine.

As a summary, there is still a great need for cost-effectivebiomaterials with adequate mechanical properties. Therefore, a goal ofthe present invention is to satisfy this need by developing a newbiopolymer and biodegradable composite material with interestingproperties such as an increased strength and toughness, by identifying amethod for increasing the impact strength of natural proteins and fibersand by producing new biodegradable composite materials. This inventiondescribes a method to improve the impact properties of glutenbiopolymer, enabling broader usage of gluten in industrial applications.This invention also describes a new composite material and a process tomake fully biodegradable composite materials.

Polythiols are molecules with multiple thiol groups in their structureand they are used for many reasons such as in the production ofdifferent polymers. The applications of these polymers includecompositions for special coatings, inks and optical devices. Polythiolsas crosslinking agents often influence the thermal and mechanicalproperties of the resulting polymers. In the prior art however,polythiols have not been used with natural polymers such as gluten.

SUMMARY OF THE INVENTION

The present invention relates to a new gluten polymer matrix, withtunable material properties and produced by using polythiol-containingmolecules during the preparation process. The present invention alsorelates to the use of said gluten polymer matrix for industrialpurposes. The present invention furthermore relates to a process or amethod for preparing or forming said new polymer matrix and to thegluten polymer matrix produced through this process.

The present invention also relates to a new biodegradable compositematerial comprising gluten and fiber. The present invention furthermorerelates to the use of said composite material for industrialapplications and to a process or method for preparing said compositematerial.

The present invention thus relates to a new gluten polymer (matrix)prepared by using polythiol-containing molecules. The present inventionrelates to a new gluten polymer matrix prepared by usingpolythiol-containing molecules or comprising polythiol-containingmolecules and having modified material properties. The invention relatesto a new gluten polymer matrix comprising polythiol-containing moleculesand with increased strain and strength, but with unaffected stiffness.The present invention relates furthermore to a new gluten polymer matrixwherein the gluten proteins are intermolecularly (and/orintramolecularly) covalently linked through a linker, more in particularthrough polythiol-containing molecules. The polythiol-containingmolecules are crosslinking the gluten proteins. In a particularembodiment of the present invention, the gluten is wheat gluten.

In a particular embodiment of the invention, the polythiol-containingmolecules are selected from the group consisting of ‘TP200 3MP3’, ‘TP703MP3’ or ‘TMP 3MP3’ or structural analogues thereof. Yet anotherparticular embodiment relates to the use of polythiol-containingmolecules, more in particular branched or hyperbranchedpolythiol-containing molecules, yet more in particular a tri-thiolcontaining molecule. The polythiol-containing molecules can be used tocovalently crosslink the gluten proteins and/or to modify the glutenmaterial properties. A particular polythiol-containing molecule istri-thiol-containing polyol mercaptoester, such as “TP200 3MP3”(Perstorp Specialty Chemicals AB) (FIG. 1) or an active structuralanalogue thereof. In a particular embodiment of the invention, a mixtureof different polythiol-containing molecules is used.

The present invention relates to a process for preparing the new glutenpolymer matrix. The process comprises dispersing or mixing gluten in thepresence of polythiol-containing molecules or combining gluten withpolythiol-containing molecules in a gluten-dispersing mixture. In acertain embodiment, the process comprises the dispersion of gluten inthe presence of at least 0.01% (w/w) of a polythiol-containing moleculeversus gluten. In another embodiment of the present invention, theprocess comprises the dispersion of gluten in the presence of at least0.01% (w/w) versus gluten or maximally 15% (w/w) versus gluten of apolythiol-containing molecule. In another embodiment at least 0.1% andmaximally 1% of the polythiol-containing molecule is dipersed withgluten. In a particular embodiment of the invention the amount ofpolythiol-containing molecules used is directly proportional to theamount of cysteine in the gluten. In a particular embodiment of theinvention, the polythiol-containing molecule is used in stoichiometricalamounts relative to the cysteines in gluten in order to have as manymoles thiol from the polythiol-containing molecules as moles thiol fromthe cysteines in gluten. In a particular embodiment of the invention theamounts of gluten and polythiol-containing molecules used is such thatthere are approximately as many mole thiols from gluten as moles thiolfrom the polythiol-containing molecules in the mixture.

In a certain embodiment of the invention, the gluten can be dispersed,mixed or combined in a gluten-dispersing mixture. The gluten can bedispersed in aqueous environments such as alcohol-water mixtures oralkaline or acidic conditions, or non-aqueous environments such as puremethanol or ethanol, by using aiding agents such as hydrogen bondbreakers, chaotropic agents and detergents and by using other solventssuch as ketones or amide solvents or mixtures thereof. In a particularembodiment the gluten is dispersed under mild acidic conditions, moreparticularly in an acetic acid solution, yet more in particular indilute acetic acid and still more in particular in 0.05 M acetic acid orthe gluten in dispersed under mild alkali conditions. In anotherparticular embodiment the gluten is dispersed in an alcohol-watermixture, more in particular in 50% (v/v) propanol-water solution or in70% (v/v) ethanol-water solution.

In another embodiment of the invention, the process for the preparationof the new gluten polymer also comprises an isolation step. In a certainembodiment the isolation step consists of precipitating the proteins ora fraction thereof, for example by changing the pH of the dispersion, bychanging the concentration of one of the solvents used or by changingthe ionic strength of the mixture. In a particular embodiment of theinvention, the precipitation is obtained by increasing the pH from acidconditions, more in particular mild acid conditions (pH 3-4) to aneutral pH (6-8) or even higher, more in particular by using NaOH, moreparticularly dilute NaOH. In another embodiment the isolation stepcomprises the precipitation of the proteins and subsequentcentrifugation.

In a further embodiment of present invention a precipitate of glutenmodified by the polythiol-containing molecule, in particular by atri-thiol-containing polyol mercaptoester and more in particular by theTP200 3MP3, can be formed by increasing the pH of the mixture from acidconditions to a higher pH until the precipitation occurs, a fraction ofthe proteins has precipitated or the precipitation is complete (neutralor alkaline conditions), more in particular by changing the pH from 3-5to 6-8.

Alternatively a method can be used wherein an alcohol-based aqueoussolution is used, particularly a 50% (v/v) propanol solution fordispersing the gluten together with the polythiol-containing moleculeand that the precipitation is obtained by adding more propanol.

Yet another embodiment of the process comprises the drying of thedispersion or the precipitate, centrifugated or not, by for exampledrying on the air, drying with hot air, spray-drying or freeze-dryingwith or without a precipitation step or centrifugation.

In yet another particular embodiment, the process for the preparation ofthe new gluten matrix also comprises a compression-molding (and/orthermo-molding) step, thereby applying pressure and a temperature raise.The new matrix can be placed in a mold and processed at a variety ofdifferent pressures and temperatures. The compression molding-stepconsists of compression-molding the protein for several minutes, rangingfrom 1 to 20 minutes, more in particular from 5 to 15 minutes and yetmore in particular for 10 minutes. In a certain embodiment of theprocess the compression-molding is performed at a minimum temperature of100° C. and a minimum pressure of 2 bars for minimum 1 minute. Inanother embodiment the compression-molding step is performed at 150°C./5 bars or 25 bars for 10 minutes. In another particular embodimentthe process comprises a subsequent cooling, more in particular to atemperature below 40° C., more in particular below 30° C. over a timeperiod between minimum 1 minute and maximum 20 minutes. An object ofthis embodiment relates to cooling below 40° C. over a period of atleast 15 minutes and yet more in particular to a temperature below 20°C. over a period of 5 minutes.

In a very particular embodiment of the present invention, there is atime period between the dispersing of the gluten in thegluten-dispersing mixture together with the polythiol-containingmolecules, the precipitation and centrifugation and/or evaporation andthe drying at one side and the compression-molding at the other side. Inthis particular embodiment there is a time period that the driedmaterials can not be handled before the compression molding step. Thistime period that the dried material is left unhandled beforecompression-molding is at least one week (7 days) or at least 30 days or60 days or 90 days or between 30 days and maximally 180 days. Thetemperature for on which the material is aged is in a particularembodiment room temperature. In another embodiment this temperature ishowever under 25° C. or higher than 25° C., more particularly higherthan 40° C.

The present invention furthermore relates to a process for preparing anew gluten biopolymer with modulated mechanical properties, more inparticular with modulated strength and strain and/or stiffness, and yetmore in particular with an increased strength and strain and unmodulatedstiffness.

The present invention also relates to a process for improving the impactproperties of gluten biopolymer with the inclusion of low levels of apolythiol-containing molecule into the gluten biopolymer dispersion.

The present invention furthermore relates to a method for preparing orforming a biodegradable article or a new gluten based polymer comprisingthe steps of dispersing and mixing the gluten in a polythiol-containingmolecule containing gluten-dispersing mixture, precipitating thereaction products out of the medium, centrifuging the mixture, dryingthe precipitate, leaving the dried material unhandled for a certain timeperiod and compression-molding the precipitate or a selection orcombination hereof. The present invention also relates to a method forpreparing a new gluten based polymer comprising the steps of dispersingand mixing the gluten in a polythiol-containing molecule containinggluten-dispersing mixture, drying the mixture, leaving the driedmaterial unhandled for a certain time period and compression-molding thedried mixture or a selection or combination hereof.

In a particular embodiment of the present invention, the strength of thegluten polymer is at least 25 Mpa and more particularly at least 30 Mpa,while the strain is at least 0.04, more particularly 0.05, while thestiffness is between 500 and 1500 MPa or not higher than 1500 MPa or norlower than 500 MPa.

The present invention also relates to a new composite materialcontaining fiber, characterised in that the fiber is coated with gluten.The new composite material therefore comprises fiber on which gluten isadhered. In a particular embodiment of the invention, the fibers used inthe composite material are selected from synthetic fibers, woodenfibers, nonwood fibers, natural fibers, biodegradable fibers or otherfibers comprising cellulose, lignin and/or pentosans. In a moreparticular embodiment, the fiber is flax fiber or glass fiber. In aparticular embodiment, the fibers used in the invention are long fibers.

The present invention also relates to a process or method for preparingsaid new composite materials. The present invention furthermore relatesto a process for preparing the gluten-coated fiber, comprising the stepsof pre-coating the fiber with gluten (under dry circumstances), thancontacting the pre-coated fiber with a gluten-dispersing mixture (e.g.aqueous medium or non-aqueous medium which has the capacity to dispersegluten), more particularly with a neutral (pH around 7) aqueous mediumand drying the resulting material, followed or not with acompression-molding step. The invention also relates to a process forpreparing the gluten-coated fiber, comprising the steps of placing thefiber (not pre-coated) together with the gluten, with or withoutpolythiol containing molecules, in an aqueous medium or non-aqueousmedium which has the capacity to disperse gluten, more particularly in aneutral (pH around 7) aqueous medium and drying the resulting material.The gluten used in the preparation of gluten-coated fibers can beunmodified commercial gluten, gluten derivatives or fractions ormodified gluten prepared by applying polythiol-containing molecules withthe process described above in dry state or wet state.

In a particular embodiment of the process for preparing the glutencoated fiber, the pre-coating of the fiber can be performed bycontacting the fiber with gluten or by bringing the gluten powder ontothe fiber, by sprinkling, by using the “fluidized bed” technology, byapplying pressure, or by any known method in the art. In anotherembodiment of the process for preparing the gluten coated fiber, thegluten pre-coated fiber is contacted with or placed in agluten-dispersing mixture like water (acidic, alkaline or neutral), morein particular water with a pH around 7, for some time, more inparticular for several seconds to minutes.

Alternatively, the present invention relates to a process for preparinggluten-coated fiber, comprising mixing a fiber in a dispersion ofgluten, precipitating the gluten onto the fiber and drying the resultingmaterial. In a particular embodiment of this process, the fibers aremixed in a dispersion of gluten, with or without polythiol-containingmolecules. In the case the fibers are dispersed with gluten withoutpolythiol-containing molecules, the gluten used can already have beenmodified by polythiol-containing molecuels by the processes describedabove. In a certain embodiment of the invention, the gluten can bedispersed as described above in a gluten-dispersing mixture, underalkaline or acidic conditions or other aqueous environments such asalcohol-water mixtures, in non-aqueous environments such as puremethanol or ethanol, by using aiding agents such as hydrogen bondbreakers, chaotropic agents and detergents and by using other solventssuch as ketones or amide solvents. In a particular embodiment the glutenis dispersed under mild acidic conditions, more particularly in anacetic acid solution, yet more in particular in 0.05 M acetic acid. Inanother particular embodiment the gluten is dispersed in a alcohol-watermixture, more in particular in a 50% (v/v) propanol-water solution.Following, the gluten can be precipitated onto the fibers or thesolvents can be evaporated from the mixture. In a particular embodimentof the process, the gluten is precipitated by changing the pH toapproximately neutral or by changing the concentration of the solvents.Yet another embodiment of the process comprises the drying of thedispersion, by for example drying on the air, spray-drying orfreeze-drying with or without a precipitation step or centrifugation.

In another particular embodiment, the above mentioned steps can befollowed by a time period that the material is left unhandled and acompression-molding step as described above.

A further embodiment of present invention is a process to form acohesive gluten polymer network around fibers. Fibers are covered bygluten powder (in certain embodiments 1/1 w/w) and consequentlycontacted for a certain period (for instance 30 second) with agluten-dispersing mixture like water (acidic, alkaline or neutral), morein particular deionised water, more in particular in water with a pHaround 7 or water with base, particularly NaOH or by contacting saidgluten powder covered fibers with alkaline water, preferably deioinsedwater with a pH of at least 8 or higher for instance by dipping saidmixture of said fibers and said gluten powder for less than one minutein said water. FIG. 4 demonstrates gluten coated fibers obtained byimmersing fibers with gluten powder in alkaline water for less than aminute. The fibers can be synthetic fibers (e.g. polypropylene fibers orpolyethylene fibers) wooden fibers or nonwood fibers (e.g. flax fibers),a combination of wood and nonwood fibers, natural fibers, biodegradablefibers or other fibers comprising cellulose, lignin and/or pentosans.The wood fibers or nonwood fibers can be unmodified natural fibers orcan be chemically modified. The gluten biopolymer stays on the fiberseven after the gluten-fiber mixture is dried (FIG. 5).

An alternative approach of gluten coating of fibers is to immersenatural wood or nonwood fibers in a gluten dispersion (as describedabove), in particularly in an aqueous environment, such as dilute acid,dilute alkali or dilute alcohol gluten solution. The soluble glutenmolecules are allowed to interpenetrate the swelling fibers. Optionallypolythiol-containing molecules can be added above 0.5% (w/w), about 0.5%(w/w), from 0.5% to 0.1% (w/w), less than 0.1% (w/w), above 0.1% (w/w),above 1% (w/w) and not more than 6% (w/w). By changing the pH, mixingother solvents like ethanol or solvent evaporation a strong adhesivebound is formed between the natural fibers and the gluten.

In yet another particular embodiment, the process for the preparation ofthe new gluten coated fiber matrix also comprises a compression-moldingor thermo-molding step as described above. This fiber/gluten matrix canbe compression-molded, for instance for 10 minutes at 150° C. at apressure of between 2 and 200 bars and cooled to form a fiber reinforcedgluten polymer article.

The new gluten polymer matrix of the present invention is optionallyprepared without the use of a plasticizer, besides thepolythiol-containing molecules and/or water used in the process. Theprocess for preparing a gluten polymer comprising the step of mixing thegluten in an aqueous environment with polythiol-containing molecules,optionally excludes the use of a plasticizer besides thepolythiol-containing molecules and/or water used in the process. Thisprocess furthermore optionally excludes the heating of the mixture ofthe gluten and the polythiol-containing molecules in an aqueousenvironment before the compression molding step. In another particularembodiment, the process of the invention could also be performed withthiol-containing molecules, more in particular the process involvingpre-coating fibers with gluten.

The present invention furthermore relates to the industrial use of theabove described biodegradable materials. The materials can for examplebe used in the automotive, food or medical industry as materials for theconstruction of cars, as packaging material or as material for theconstruction of medical devices respectively. Solid, non-ediblebiodegradable gluten based articles have a wide area of applications andindustrial use. Biodegradable products (in a relatively short perioddestructible) or polymers can be used in eating utensils, cups, plates,sheet items, packaging and other convenience products, presently mostlyfabricated by indestructible polymers.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1. Schematic of the polyol mercaptoester, TP200 3MP3, m+n+o=20.

FIG. 2. Photograph of an unmodified gluten specimen (left) and TP2003MP3-modified-gluten specimen (right) obtained by the methods described.These materials were compression-molded for 10 minutes at 150° C. at apressure of 25 bars. The temperature of the press was subsequentlydecreased to 20° C. before the mold was removed from the press and theparts demolded.

FIG. 3. Extruded parts of various geometries made from glutenbiopolymer.

FIG. 4. A photograph of flax fibers covered with gluten powder, forillustrative purposes only. In the actual experiment, the flax fiberswere coated manually by rolling them in the gluten powder. Afterwards, astrainer was used to support the gluten powder-coated fibers as theywere immersed in a 45° C. alkaline (pH=11) water bath for 30 seconds.

FIG. 5. A photograph of the gluten biopolymer/flax fiber bundlecomposite formed after the gluten polymer formed a precipitate aroundthe flax fibers. After two days, the gluten matrix was rigid, as most ofthe moisture inside the gluten polymer network had evaporated.

FIG. 6. Comparison of mechanical properties of native gluten (sample 20)and thiol-modified gluten (sample 22).

FIG. 7. Water absorption measurements with plain gluten and preparation22 (as described in example 6). The data indicate a difference inmolecular structure between the plain gluten and the thiol-treatedgluten.

FIG. 8. SE-HPLC data for different samples in order to evaluate theinfluence of thiol-modification and molding.

-   a. SE-HPLC data for several unreduced samples (thiol-modified or not    and molded or not)-   b. SE-HPLC data for the same samples as in FIG. 8 a but after    treatment with dithiotreitol (DTT).    The figure indicates that molded samples contain less monomers and    more SDS-unextractable polymers than unmolded samples. This suggests    more extensive crosslinking of the polymers and incorporation of    gliadins into the polymers as a result of the molding process    (pressure and temperature raise). The figure also shows that    incubation with a thiol-containing molecule results in lower size    polymers and a higher level of monomers before molding suggesting    that the thiol-containing molecule acts as a reducing agent and    breaks disulfide bridges. After molding, however, samples with the    thiol-containing molecule had even lower levels of monomers and    higher levels of SDS-unextractable polymers than molded samples    without the thiol-containing molecule suggesting even more extensive    cross-linking as a result of the presence of the thiol-containing    molecule.

FIG. 9. Mechanical properties of molded gluten specimens (as used inFIG. 10): Strain-to-failure and strength.

-   a. Mean values of % strain at break illustrating increase in    strain-to-failure as the gluten formulations aged with time. The    first and the third bars from the left depict specimens molded from    unmodified powder, while the second and fourth bars represent    specimens molded from tri-thiol-modified gluten powder. The two last    bars from the left represent samples molded and tested long after    preparation of the dry material (in July), while the two first bars    from the left illustrate specimens that were molded and tested three    months before (in april of the same year), namely shortly after the    preparation of the dry material. The error bars are equivalent to    one standard deviation.-   b. Mean values of strength illustrating a similar increase in    strength as the gluten formulations aged with time (the samples were    left unhandled for a period of time before molding).

FIG. 10. Mechanical properties of molded gluten specimens:Strain-to-failure

-   a. Samples 20, 20 b and 25 are native gluten, while samples 22 and 4    were made using stoichiometric amounts of thiol with respect to the    cysteines in gluten. Specimens were molded in April, shortly after    they were prepared.-   b. Samples 25 b, 25 c, 30 and 30 b are native gluten, while sample    22 b was made using stoichiometric amounts of thiol with respect to    the cysteines in gluten. Specimens were molded 3 months later than    the samples of FIG. 10 a.-   c-d. Additional data illustrating changes in mechanical properties    due to the addition of fiber (#18) or different thiol-containing    molecules in different amounts [cysteine (#21, #26), DTT (#27), TP70    3MP3 (#2, #23) and TP200 3MP3 (#22, #4, #28)].    25 b, 25 c, etc. in the figure indicate a second or third molding    from the same preparations. H, D, and W indicate measurements    acquired one hour, one day or one week after molding.

FIG. 11. Mechanical properties of molded gluten specimens: Strength Forthe same samples and under the same conditions as in FIG. 10.

FIG. 12. Mechanical properties of molded gluten specimens: Stiffness Forthe same samples and under the same conditions as in FIG. 10.

FIG. 13. Picture of mold without and with a gluten sample.

DETAILED DESCRIPTION OF THE INVENTION

The terminology used herein is for the purpose of describing particularembodiments only, and is not intended to limit the scope of the presentinvention.

Definitions

As used in the specification and the appended claims, the terms “fibers”and “fibrous materials” include both inorganic fibers or fabric andorganic fibers and fabric. In general, fibers can be classified intothree categories: wood, nonwood, and nonplant.

Fibers that may be incorporated into gluten matrix preferably includenaturally occurring organic fibers, such as cellulosic fibers extractedfrom hemp, cotton, plant leaves, sisal, abaca, bagasse, wood (bothhardwood or softwood, examples of which include southern hardwood andsouthern pine, respectively), or stems, husks, shells, and fruits or anynonwood fiber as defined hereunder, or inorganic fibers made from glass,graphite, silica, ceramic, or metal materials. Any equivalent fiberwhich imparts strength and flexibility is also within the scope of thepresent invention.

The term “nonwood fibers” as used herein is thus to distinguish plantfibers from wood fibers (softwood or hardwood), the fibers can bederived from selected tissues of various mono- or dicotyledonous plants.And are categorized botancially as grass, bast, leaf, or fruit fibers.The nonwood fibers can also be classified by means of production such assugar cane bagasse, wheat, straw and corn stalks byproducts. They canalso be grouped as “fiber plants”, plants with high cellulose contentthat are cultivated primarily for the sake of their fibers such as jute,kenaf, flax, cotton and ramie. An example of nonwood fibers are fibersconsisting of the group of Jute, flax, cotton, Hemp, Kenaf, Pina, Abaca,Sisal, Hennequen, Stalk (Rice, Wheat, Barley, Oat, Rye), Cane (Sugar,Bamboo), Grass (Esparto, Sobai), Reed (e.g. Phragnites communis), Bast(Seed flax, Kenaf, Jute, Hemp, Ramie), core (Kenaf, Jute), Leaf (Abaca(e.g. Manila), Sisal (e.g. Agave)), Seed hull (e.g. cotton linter).

In a particular embodiment the fibers used are long fibers (longer than2 to 3 cm) or optionally short fibers are excluded.

The term “polythiol-containing molecule(s)” as used herein refers tomolecules with at least two free thiol groups. In particular embodimentsthe polythiol-containing molecules have at least three free thiolgroups, particularly thiol groups that have a free electron pair and ina particular case have reducing capacity. The molecules can be straight,branched or hyperbranched. In a particular case, thepolythiol-containing molecules have thiol groups that are separated fromeach other so that they can not easily react intramolecularly. Examplesof polythiol-containing molecules are ‘TP200 3MP3’, ‘TP70 3MP3’ or ‘TMP3MP3’ (Trimethylolpropane Tri(3-mercaptopropionate)) (PerstorpSpeciality Chemicals, Aldrich Chemicals), the three last ones differingwith respect to their degree of ethoxylation (the first carries twentyethylene oxide units, the second carries seven, and the last does notcarry any ethylene oxide units at all). ‘TP200 3MP3’ has a highflexibility and water compatibility. Other examples are dithiotreitol,Glycol Dimercaptoacetate, Glycol Dithioglycolate, GlycolDi(3-mercaptopropionate), Pentaerythritol, Tetramercaptoacetate,Pentaerythritol Tetrathioglycolate, PentaerythritolTetra(3-mercaptopropionate, Trimethylolpropane Trimercaptoacetate,Trimethylolpropane Trithioglycolate, TrimethylolpropaneTri(3-mercaptopropionate), Trimethylolethane Trimercaptoacetate,Trimethylolethane Trithioglycolate, TrimethylolethaneTri(3-mercaptopropionate, Di-Trimethylolpropane Tetramercaptoacetate.Other polythiol-containing molecules can be synthesized byesterification of a polyol such as glycol, pentaerythritol,trimethylolpropane, trimetylolethane or di-trimethylolpropane with forexample mercaptocarboxylic acids such as mercaptobutyric acid. Thesynthesis of polythiol-containing molecules out of polyols is alsodescribed in the prior art. In a particular embodiment of the invention,peptides or proteins containing multiple cysteines could also serve aspolythiol-containing molecules. The term polythiol-containing moleculesoptionally excludes thiol redox proteins such as thioredoxin orglutaredoxin.

The term “thiol-containing molecules” refers to molecules with at leastone free thiol group.

The term “gluten” as used herein refers to the commercially availablewheat gluten from for example Amylum (Aalst, Belgium). The term glutenhowever also refers to gluten as a composition containing gliadins andglutenins in different amounts. It is however clear to a person skilledin the art that gluten as used in this invention can also mean anycomposition containing at least 20% storage proteins derived from aplant, or more particularly from a seed (e.g. soy) or a cereal, yet moreparticularly from a prolamine rich cereal (wheat, maize, barley,sorghum, millets, rye) or in particular from wheat, maize, rice, barley,sorghum, millets, rye or oats. The term can also refer to fractions ofal the above described compositions and derivatives or modified gluten(chemically or enzymatically).

It is also clear to a person skilled in the art that “gluten” could alsorefer to a synthetic mixture which is analogous to the gluten obtainedfrom naturally occurring plants.

The term “gluten-dispersing mixture” refers to any mixture comprising atleast one liquid or solvent that is able to at least disperse gluten.The gluten dispersing mixture refers also to mixtures able to solubilizeor dissolve gluten. Gluten can be dispersed in aqueous environments suchas alcohol-water mixtures in different percentages. Gluten can also bedispersed under aqueous alkaline or acidic conditions or non-aqueousenvironments such as pure methanol or ethanol, by using aiding agentssuch as hydrogen bond breakers, chaotropic agents and detergents and byusing other solvents such as ketones or amide solvents or mixturesthereof. Examples of gluten dispersing mixtures are mild acidicconditions like a (dilute) acetic acid solution, mild alkali conditions,alcohol-water mixture of 50% (v/v) propanol or 70% (v/v) ethanol, andsome gluten is dispersable in pure methanol.

Description

The present invention shows that gluten can be formed into a toughplastic like substance with interesting properties by usingthiol-containing molecules during its preparation. This led to thepossibility of developing biodegradable high performance engineeringplastics and composites from renewable resources that are far lessexpensive than their synthetic counterparts. The present inventionshowed that an otherwise brittle protein-based material can be toughenedby increasing the yield stress and strain to failure, withoutcompromising stiffness.

In the present work, the fracture toughness of the gluten polymer wasimproved by a factor of ten or more with the addition of apolythiol-containing molecule such as a tri-thiol-containing modifyingagent and by applying the rest of the process of the invention (i.e.aging). The polythiol-containing molecules have another notableattribute, namely, that under proper chemical and environmentalconditions, they have the potential to bond chemically with the glutenbiopolymer via sulfhydryl/disulfide exchange reactions, giving rise to apotentially more stable material (e.g. a stabilized gluten foam). Inaddition, the process does not require the addition of other agents,such as plasticizing agents or salts. The water absorption data (FIG. 7)show to the fact that the polythiol-containing molecules arecross-linked with the gluten proteins.

The amount of polythiol-containing molecules used in the process can becalculated in regard of the amount of cysteines (free and involved indisulfide bonds) in the gluten. The amount of cysteines in a protein orin gluten can easily be determined by applying methods known in the artlike the automated Edman degradation procedure using phenylisothiocyanate (PITC) or the acid hydrolysis combined with ion-exchangechromatography and detection with the use of ninhydrin. The amount ofcysteines in gluten can also be found in literature and is around 13.82mmole cysteines per 100 g gluten. The amount of thiol groups in amolecule can easily be calculated, so that for example thepolythiol-containing molecule TP200 3MP3 contains 2.35 mmol SH per gmolecule. Starting from these data the amounts used of gluten andpolythiol-containing molecules can be calculated to havestoeichiometrical amounts. 5.8% (w/w) TP200 3MP3 corresponds thereforestoichiometrically to the amount of thiol groups in gluten. The same for3.2% (w/w) of TP70 3MP3, 1% (w/w) of DTT and 1.7% (w/w) of cysteine.

The present invention relates to the incorporation ofpolythiol-containing molecules, for instance TP200 3MP3 from PerstorpSpecialty Chemicals AB, into the gluten biopolymer and to thecrosslinking of the polythiol-conatining molecules with the glutennetwork, giving rise to a tougher material system. Inherent challengesin processing gluten are attributed to the low solubility of gluten inmost solvents, as well as its high melt viscosity.

Results of the research showed that when a thiol-containing molecule wasused in the preparation of the gluten polymer and incorporated into thenetwork structure of the gluten polymer, material's strain-to-failureand strength can be increased without compromising stiffness (FIGS. 10,11 and 12). Furthermore, water absorption results indicate that thepresence of a thiol-containing molecule leads to an increase inmolecular crosslink density (FIG. 7). Finally, HPLC data of moldedthiol-modified gluten are consistent with that of a polymer that hasbeen further crosslinked (FIG. 8).

The improved strain and strength of polymers of the present inventionand obtained by the process of the present invention can be deduced fromexperiments performed. Comparing samples prepared withpolythiol-containing molecules wath native molded gluten or even samplesprepared with cysteine, shows an increase in strength and strain, andeven more when stress and strain would be looked at together.

Another important aspect is that the results show that there is acertain ageing effect that further improves the mechanical properties ofthe new gluten biopolymer (FIGS. 9, 10, 11 and 12). Mechanical studiesshowed that ageing the powdered gluten formulations for two or three tosix months leads to an increase in both strength and strain-to-failureof molded specimens. This can be observed through direct comparisonbetween the set of unmodified and modified specimens molded and testedin the spring (April-June) with the second series of specimens, whichwere molded and tested around 3 months later during the summer(July-August) as shown in FIGS. 9 a and b and 10, 11 and 12. Both setsof specimens were molded from the same set of powders formulated in theFebruary to April time period. In general, the results show that themodified wheat gluten polymer has properties approaching that ofpolypropylene and epoxies, which could very well continue to improvewith time.

The research also resulted in the development of glutenbiopolymer-modified fiber (flax or glass) and bundle, demonstrating aprocess to make fully biodegradable composite materials. Qualitativeanalysis suggests that a strong interface between the natural fibers andbiopolymer matrix can form spontaneously under the proper conditions,precluding the need to rely on more traditional chemical treatments topromote fiber/matrix adhesion. The present methods that are descrobed inliterature mostly can only handle short fibers (maximally approximately2-3 cm). This method is able to handle long fibers. Some moldingtechniques as used in U.S. Pat. No. 5,665,152 (injection molding) arenot able to handle long fibers.

In order to be able to chemically modify gluten or to coat gluten onfibers, gluten needs to be dispersed. Several methods for thepreparation of chemically modified gluten or gluten coated fibersdescribed, use a dispersion of gluten. Several methods and agents can beused to obtain a dispersion of gluten:

-   -   (Mild) acidic/alkaline conditions: Probably the most gentle way        to disperse gluten, is to bring the gluten in an aqueous        environment at a relatively low pH. Decreasing the pH (to around        4 or lower, with for example dilute HCl, (dilute) acetic acid or        lactic acid) allows to solubilize a part of the gluten proteins        and surely allows to make a homogenous “dispersion” of the total        gluten. Also alkaline conditions (e.g. aqueous NaOH) allow to        make a homogenous dispersion.    -   However, stong alkaline or acid conditions will further help        solubilizing gluten but will affect the protein structure        (deamidation, modification of some amino acids, peptide bond        hydrolysis, etc.).    -   An advantage of dispersing under (mild) acidic or alkaline        conditions is that proteins can be precipitated by a simple        change in pH towards neutral where gluten proteins are totally        insoluble. This type of precipitation can than be applied after        putting fibers in a gluten dispersion to make the gluten        proteins efficiently stick to the fiber material.    -   Aqueous alcohol solutions: Alcohol/water mixtures are very often        used in gluten research to solubilize part of the gluten        proteins (ca 50% can be solubilized) and the total gluten can be        homogenously dispersed in alcohol/water mixtures. Mixture of 70%        ethanol or 50% propanol can for example be applied for this        purpose. Some other proteins, like for example corn zeins (the        “gluten” equivalent from corn) are soluble in pure methanol.    -   The fact that gluten proteins are only soluble/dispersible at        certain alcohol concentrations offers the possibility to        precipitate them by changing this concentration (adding more        alcohol or by dilution with water). The alcohol can also be        removed by evaporation.    -   aiding agents: Several agents are often used in gluten research        either in pure water or in one of the above solvents to aid        solubilization of gluten proteins. Often several agents are        combined to solubilize gluten proteins. However, protein        structure is nearly always affected in this way.    -   Following aiding agents are used:    -   a/ reducing agents (e.g. sulfites, cysteine, glutathione,        dithiothreitol): by lowering the molecular weight of the        proteins they enhance their solubility (obviously they also        drastically change their structure and functionality)    -   b/ hydrogen bond breakers (e.g. urea)    -   c/ chaotropic agents (e.g. guanidinium hydrochloride)    -   d/ detergents (e.g. sodium dodecyl sulfate, cetyl trimethyl        ammonium bromide)    -   e/ salts: increasing the ionic strength is known to decrease the        solubility of gluten proteins.    -   However, in the literature it can also be found that incubation        of gluten in salt would subsequently increase the solubility of        gluten proteins in distilled deionized water.    -   other solvents: Literature describes the use of other solvents        (e.g. ketones, amide solvents) for these purposes (e.g.        solubilization of zeins).

Drying of materials can be performed in several ways as known in theart. Materials can be dried on the air, with hot air, by usingspray-drying or freeze-drying. The materials can also be placed in andessiccator or a heating gun, combined with water attracting compounds.The solvents in a mixture can furthermore also be evaporated by using arotovapor, or by applying vacuum. Spray-drying can for example beperformed under the following conditions: compressed air P=4 bars; inletT=130° C. and outlet T=95-105° C.

The fluidized bed technology can also be used in the invention in orderto pre-coat the fibers with gluten. With for example ETI's E-Preg®process, carbon fiber or fiberglass fabric is passed through a specialelectrostatic fluidized bed coater capable of depositing (gluten) powderon both sides of the web. Electrostatic attraction causes the powder toadhere to the substrate, which is then passed through an oven to meltand flow the powder into or onto the fiber.

General Methods and Materials

Commercial wheat gluten from Amylum (Aalst, Belgium) was used in thisstudy. The protein content of this gluten can be determined with theDumas method or the Kjeldahl-method.

Preparation of a New Gluten Biopolymer by Using Thiol-ContainingMolecules

The chemical modification of gluten can in general be obtained throughmixing gluten with a thiol-containing molecule in an aqueous medium. Bysubsequent compression molding a material with modified properties isobtained.

The thiol-containing molecules were added in amounts calculated withrespect to the experimentally determined cysteine content in the gluten(gluten contains approximately 13.8 mmol thiol function—this can bederived from the amount of cysteine in gluten). As an example, theprinciple of a 1:1 stoichiometric mixture can be applied to allow onemole of TP200 3MP3 SH groups to interact with one mole of glutencysteine groups. The basic procedure involved preparing a glutendispersion containing the thiol-containing compound and leaving themixture to stir overnight, mostly in a refrigerator (6-8° C.). Thefollowing day the contents were dried (i.e. freeze-dried) over a certainperiod (i.e. four days). Afterwards, the dried contents were homogenizedusing a mortar and pestle, passed through a micron-size sieve, and puton a rotating shaker overnight. Specific details pertaining toindividual samples are provided below.

Compression Molding—Thermo Molding

Compression molding was performed with reference gluten samples,thiol-modified gluten and gluten coated fibers to produce a moldedmaterial. Specimens and gluten samples can be compression molded byapplying a certain pressure and temperature, i.e. at 5 bars/150° C. for3 to 15 min. Specimens were prepared in a 10 cavity mold. The mold wascarefully prepared using a mold release agent, previously applied andcured before gluten powders were used.

Preparation of Gluten Coated Fibers

The general method used in order to obtain a gluten coated fiber was tobring the fiber into contact with gluten in a gluten-dispersing mixture(first pre-coating the fiber with gluten in the dry state and thancontacting with a gluten-dispersing mixture or mixing fibers with glutenin a gluten-dispersing mixture). In one method the gluten is pre-coatedwith gluten powder by bringing gluten in contact with the fibers, forexample by sprinkling or by the fluidized bed method.

Mechanical Properties Determination

Tensile Test: The 10 specimens prepared from each molding exercise wereused in tensile tests. Specimens were tested within 1 hour of molding,after 24 hours, and after 7 days. At each testing time, 3 of thespecimens were used. All specimens were stored at ambient conditions sothe tests after 24 hours and after 7 days provide preliminaryindications of temporal stability of the material. The tests wereconducted on a computer interfaced Instron 1011 with a 1000 Lb loadcell. Load data were collected at a rate of 10 s⁻¹, and each test wasrepeated 3 times. The stress strain curves were evaluated to providemodulus, failure strain, and yield strength. Modulus was determined byfitting a straight line to the stress strain curves in the early regionat strains below ½%.

Charpy Impact test: For the measurement of fracture toughness, theCharpy impact test was conducted in accordance with ISO-Norm 179.

Three point bend test: the three point bend test was performed asdescribed in literature and is well known to a person skilled in theart.

Water absorption studies: the water absorption studies were performed asdescribed in literature and is well known to a person skilled in the art

Molecular Weight Determination: Size Exclusion—High Performance LiquidChromatography (SE-HPLC)

Samples were dissolved (1 mg/ml) in 0.05M sodium phosphate buffer (pH6.8), containing 2.0% (w/v) sodium dodecyl sulphate (SDS), filtered(0.45 μm) and a fraction was loaded on a Phenomenex BioSep-SEC-S4000(300 mm×7.8 mm) column (Phenomenex, Torrance, Calif., USA). The proteinswere eluted at room temperature with 50% (v/v) acetonitrile containing0.05% (v/v) trifluoroacetic acid (flow rate: 0.5 ml/min). Reducedprotein samples were obtained by adding 1% (w/v) dithiothreitol to thephosphate-SDS buffer. The detection was performed with a Kontron HPLC332 detector (Kontron Instruments Ltd, Buckinghamshire, UK) at 210 nm.Proteins were classified into three groups: insoluble polymeric protein,soluble polymeric protein, and monomeric protein. The proportion ofinsoluble protein was calculated from peak areas of reduced andunreduced samples in the chromatograms (Verbruggen, I. M. et al., J.Cereal Sci. 2003, 37, p. 151).

EXAMPLES

Comparison of the mechanical properties of plain gluten (e.g. impactstrength) with those of several synthetic materials, comprisingpolypropylene, epoxy, low-density polyethylene (PE), and high-densitypolyethylene PE can be found in the literature (Table 1). TABLE 1Mechanical properties of various polymers as they compare with glutenmatrix material processed at 150° C./72 bars as measured by theThree-Point-Bend test. Charpy Impact Strength Polymer (kJ/m²) Gluten2.48 Polypropylene 14 Epoxy 7.5 Low density PE 39 High density PE 68

According to the literature the apparent E-modulus and tensile strengthof wheat gluten seems on par with a number of commonly used syntheticpolymers. However, a drawback is the fact that the impact strength ofcured gluten is relatively low. The impact strength increased whenglycerol was added to the matrix, however this results in the loweringof the E-modulus and tensile strength.

The different examples that are given and the data presented are clearlyvarying with the concentration of thiol-containing molecules and thetime before molding and time before measuring (“ageing effects”).

Example 1

The polythiol-containing molecule, ‘TP200 3MP3’, was employed in thisexample. Gluten powder (150 g) was added slowly (over a period of 1½ hrsat room temperature) to 1.5 L 0.05 M acetic acid solution containing0.1% (w/w) of ‘TP200 3MP3’. The mixture was stirred continuously as thegluten powder was added to the solution. The dispersion was put on ashaker in a refrigerator and left overnight. A homogenous dispersion ofthe gluten proteins in dilute acetic acid was obtained, enabling the‘TP200 3MP3’ molecule to interact directly with the gluten proteins. Thematerial was recovered by precipitation upon increasing the pH (from4-4.5 to 6.5-7) by addition of dilute NaOH. Afterwards, thegluten/solvent mixture was separated by centrifugation (10,000 g, 20°C., 15 min) and the modified-gluten precipitate was dried and stored ina refrigerator until further use. The molded material could than beobtained by compression molding the previously prepared powder.

Example 2

In this experiment, a 50% (w/w) propanol-water solution was used inplace of dilute acetic acid, and the solvent was evaporated by‘rotavapping’ the modified-gluten/solvent mixture at 50° C. However,subsequent removal of the dried biopolymer from the glass flask wasdifficult due to the strong adhesion between the gluten network and theglass. To be able to easily remove the biopolymer dilute acetic acid canbe added, before all the propanol is evaporated. Upon incorporating 0.1%(w/w) of ‘TP200 3MP3’ in a 50% (v/v) propanol-water solution, thefracture toughness of molded gluten was increased from 3 kJ/m² to anaverage of 36 kJ/m² as measured by the Charpy Impact test. Specimenswere compression-molded at 150° C./25 bars for 10 min. and subsequentlycooled to 20° C. over a period of 5 min. Individual fracture toughnessmeasurements of four six-day-old TP2003MP3-modified gluten specimensyielded an average value of 36.2 kJ/m², with a deviation of around 10kJ/m². An unmodified control sample yielded a Charpy impact strength of3.2 kJ/m² (Iso Norm 179 standard analysis).

Example 3 Preparation and Investigation of Gluten Coated Flax Fibers

A bundle of flax fiber was pre-coated with gluten powder by sprinklingthe gluten powder onto the fibers, which was then placed between twometal strainers. A dilute alkaline (NaOH) water bath was prepared (asacidic conditions are known to be detrimental to flax fibers). Twostrainers were used to contain the coated fiber bundle, which was thendipped in the alkaline water bath for 30-60 sec. The hydrated glutenformed a precipitate almost immediately, resulting in agluten-encapsulated fiber bundle. The gluten-coated fiber bundle wasleft to dry in ambient conditions for a period of several days andyielded the new composite material, namely gluten coated flax fiber. Thegluten coated fibers remain intact after several months.

Example 4 Preparation of Gluten Coated Glass Fibers

For the purpose of preparing the gluten coated glass fibers, thestandard “Fiber-Tow Impregnation Line” or “Fluidized Bed” technology wasapplied. In this experiment, a commercial grade-glass fiber: “2400 P 319E1” from Owens Corning was used. The airflow of the fluidized chamberwas set at 0.2 bars and the vibration at 7 bars. The oven temperatureswere set at 120-170° C. and 175° C., respectively, and the rollersinside the oven were removed. The oven was not used to melt the gluten,but merely, to dry the fibers. As the gluten powder coated fiber wasdrawn from the fluidized bed, water was applied manually using either awater bath or a squirt bottle for bringing the gluten molecules in closeproximity with the fiber surface.

Example 5 Chemically Modified Gluten Polymers Prepared DuringExperiments with their Referred Sample Numbers

-   1) plain gluten; solvent used 0.05M AcOH; contents freeze-dried,    milled, and passed through a 250 micron sieve-   2) gluten+1% (w/w) TP703MP3; solvent used: 0.05 M AcOH; contents    freeze-dried, milled, and passed through a 250 micron sieve-   3) gluten+1% (w/w) TP200 3MP3; solvent used: 0.05 M AcOH; contents    freeze-dried, milled, and passed through a 250 micron sieve-   4) gluten+5.8% (w/w) TP200 3MP3; solvent used: 0.05 M AcOH; contents    freeze-dried, milled, and passed through a 250 micron sieve-   5) gluten+1% (w/w) TP200 3MP3; solvent used 50% PrOH; contents    freeze-dried, and homogenized with a mortar and pestle-   6) plain gluten; solvent used 70% EtOH; contents freeze-dried    (twice), homogenized with a mortar and pestle, passed through a 400    micron sieve, and put on rotating shaker overnight-   7) gluten+0.1% (w/w) DTT; solvent used: 70% EtOH; contents    freeze-dried (twice), homogenized with a mortar and pestle, passed    through a 400 micron sieve, and put on rotating shaker overnight-   8) gluten+0.1% (w/w) DTT+0.5% (w/w) KIO₃ (present in excess);    solvent used 70% EtOH; contents freeze-dried (twice), homogenized    with a mortar and pestle, passed through a 400 micron sieve, and put    on rotating shaker overnight-   9) gluten+0.1% (w/w) DTT+1% (w/w) TP200 3MP3+0.5% (w/w) KIO₃    (present in excess); solvent used: 70% EtOH; contents freeze-dried    (twice), homogenized with a mortar and pestle, passed through a 400    micron sieve, and put on rotating shaker overnight-   10) gluten+0.1% (w/w) DTT+1% (w/w) TP200 3MP3; solvent used: 70%    EtOH; contents freeze-dried (twice), homogenized with a mortar and    pestle, passed through a 400 micron sieve, and put on rotating    shaker overnight-   11) plain gluten; solvent used 70% EtOH; contents freeze-dried    (twice), homogenized with a mortar and pestle, passed through a 400    micron sieve, and put on rotating shaker overnight.-   18) gluten+6.5% (w/w) China reed fibers; solvent used 0.05M AcOH;    contents freeze-dried (twice), homogeneous on a macroscopic scale;    mortar and pestle not used to avoid fiber breakage-   19) gluten+29.4% (w/w) China reed fibers; solvent used 0.05M AcOH;    contents freeze-dried (twice), inhomogeneous on a macroscopic scale;    mortar and pestle not used to avoid fiber breakage-   20) plain gluten; solvent used 0.05 M AcOH; contents freeze-dried,    homogenized with a mortar and pestle, passed through a 400 micron    sieve, and put on rotating shaker overnight-   21) gluten+0.55% (w/w) cysteine; solvent used 0.05 M AcOH; contents    freeze-dried, homogenized with a mortar and pestle, passed through a    400 micron sieve, and put on rotating shaker overnight-   22) gluten+5.8% (w/w) TP200 3MP3; solvent used 0.05 M AcOH; contents    freeze-dried, homogenized with a mortar and pestle, passed through a    400 micron sieve, and put on rotating shaker overnight-   23) gluten+3.2% (w/w) TP70 3MP3; solvent used 0.05 M AcOH; contents    freeze-dried, homogenized with a mortar and pestle, passed through a    400 micron sieve, and put on rotating shaker overnight-   24) gluten+3.2% (w/w) TP70 3MP3+0.5% KIO₃; solvent used 0.05 M AcOH;    contents freeze-dried, homogenized with a mortar and pestle, passed    through a 400 micron sieve, and put on rotating shaker overnight-   25) plain gluten; solvent used 0.05 M AcOH; contents freeze-dried,    homogenized with a mortar and pestle, passed through a 400 micron    sieve, and put on rotating shaker overnight-   26) gluten+1.7% (w/w) cysteine; solvent used 0.05 M AcOH; contents    freeze-dried, homogenized with a mortar and pestle, passed through a    400 micron sieve, and put on rotating shaker overnight-   27) gluten+1.0% (w/w) DTT; solvent used 0.05 M AcOH; contents    freeze-dried, homogenized with a mortar and pestle, passed through a    400 micron sieve, and put on rotating shaker overnight-   28) gluten+11.6% (w/w) TP200 3MP3; solvent used 0.05 M AcOH;    contents freeze-dried, homogenized with a mortar and pestle, passed    through a 400 micron sieve, and put on rotating shaker overnight-   29) gluten+11.2% (w/w) TP200 polyol; solvent used 0.05 M AcOH;    contents freeze-dried, homogenized with a mortar and pestle, passed    through a 400 micron sieve, and put on rotating shaker overnight-   30) plain gluten; solvent used 0.05 M AcOH; contents freeze-dried,    homogenized with a mortar and pestle, passed through a 400 micron    sieve, and put on rotating shaker overnight-   31) gluten+5×[5.8% (w/w) TP200 3MP3]; solvent used 0.05 M AcOH;    contents freeze-dried, homogenized with a mortar and pestle, passed    through a 400 micron sieve, and put on rotating shaker overnight-   32) gluten+10×[5.8% (w/w) TP200 3MP3]; solvent used 0.05 M AcOH;    contents freeze-dried, homogenized with a mortar and pestle, passed    through a 400 micron sieve, and put on rotating shaker overnight-   33) gluten+15×[5.8% (w/w) TP200 3MP3]; solvent used 0.05 M AcOH;    contents freeze-dried, homogenized with a mortar and pestle, passed    through a 400 micron sieve, and put on rotating shaker overnight

Example 6 Results of Experiments

The strain, strength and stiffness of several samples has been measured.Results are shown in FIGS. 9, 10, 11, and 12. The results show anincrease in strain and strength, while the stiffness remains unaffectedfor thiol-modified gluten polymers and for gluten-coated fibers.

1-47. (canceled)
 48. A polymer of gluten comprising gluten proteins,wherein said gluten proteins are intermolecularly covalently linkedthrough polythiol-containing molecules.
 49. The polymer of claim 48,which has a strength higher than 30 MPa.
 50. A process for preparing apolymer of gluten comprising gluten proteins comprises the step ofmixing said gluten proteins in a gluten-dispersing mixture withpolythiol-containing molecules.
 51. The process of claim 50, whereinsaid gluten-dispersing mixture is an aqueous environment.
 52. Theprocess of claim 50, comprising the step of isolating said glutenpolymer by precipitation and subsequent centrifugation.
 53. The processof claim 50, comprising the step of drying said gluten-dispensingmixture comprising said gluten proteins so as to obtain a driedmaterial.
 54. The process of claim 53, comprising the step of firstageing said dried material by leaving it unhandled for a certain timeperiod and then compression-moulding said dried material.
 55. Theprocess of claim 54, wherein said time period is at least 7 days. 56.The process of claim 54, wherein said time period is at least 30 days.57. The process of claim 54, wherein said time period is about 30 daysto about 90 days.
 58. The process of claim 54, wherein said ageing isperformed at room temperature.
 59. The process of claim 54, wherein saidageing is performed at a temperature of over 25° C.
 60. The process ofclaim 54, wherein said ageing is performed at a temperature higher than40° C.
 61. A process for preparing a gluten based polymer comprising thesteps of: (a) mixing gluten in a gluten-dispersing mixture together withpolythiol-containing molecules; (b) drying the mixture resultingtherefrom so as to obtain dried material; (c) ageing said dried materialby leaving it unhandled for a certain time period; and (d)compression-moulding said dried material or a selection or combinationthereof.
 62. The process of claim 61 which comprises a step ofprecipitating the reaction products out of the mixture by mixing glutenin a gluten-dispersing mixture together with polythiol-containingmolecules and thereafter the step of centrifuging said mixture beforedrying the precipitate.
 63. A composite material comprising fibers and agluten polymer intermolecularly covalently linked throughpolythiol-containing molecules according to claim
 48. 64. A process forpreparing a composite material comprising fibers and a gluten polymer,wherein the process comprises the steps of: (a) pre-coating said fiberswith the gluten polymer of claim 48; and (b) contacting the pre-coatedfibers obtained under (a) with a gluten-dispersing mixture.
 65. Theprocess of claim 64, comprising a final step of drying the materialobtained after step (b), ageing said material by leaving said materialunhandled for a certain time period, and then compression-moulding saidmaterial.
 66. A process for preparing a gluten-fiber composite material,comprising the steps of mixing gluten and fiber in a gluten-dispersingmixture, drying the gluten-fiber mixture so obtained, ageing the driedmixture by leaving the dried mixture unhandled for at least 30 days andcompression-moulding the dried gluten-fiber mixture.
 67. A process forpreparing a gluten-fiber composite material, comprising the steps ofpre-coating fibers with the gluten polymer under dry circumstances andthen contacting the pre-coated fibers with a gluten-dispersing mixture.68. A process according to claim 67, wherein one, two or all of thefollowing steps are performed: (a) drying the gluten-coated fibers; (b)ageing said gluten-coated fibers by leaving them unhandled for a certaintime period; and (c) compression-moulding said gluten-fiber compositematerial.
 69. A composite material prepared by the process of claim 67.70. Gluten that is compression-moulded after it is aged by being leftunhandled for a certain period of time.